In an inkjet printer that forms an image by impacting minute droplets from nozzles onto a recording medium, viscosity of an ink in the nozzles is increased when discharge of the droplets is stopped for a small period of time alone, thereby leading to a discharge failure in some situations.
In an actual printing operation, there are some nozzles that keep preventing discharge of droplets depending on image data. In the prior art, a meniscus oscillation signal used for oscillating a liquid surface at a nozzle tip (which will be referred to as a meniscus hereinafter) is uniformly input to all nozzles before or after a discharge signal that is output to an inkjet head in synchronization with a print timing signal. As a result, in the prior art, the ink in the nozzles is caused to flow before or after discharge of the droplets, and viscosity is thereby lowered to stabilize the discharge. Further, in the prior art, the meniscus oscillation signal is applied even to nozzles that do not discharge droplets in synchronization with the print timing signal. As a result, an increase in viscosity of the ink in the nozzles is avoided (Patent Documents 1 and 2).